1. Field of the Invention
The present invention relates to a robotic transport apparatus suitable for transporting workpieces in a semiconductor device manufacturing system, for example, including wet and/or dirty processes such as a CMP (chemical mechanical polishing) system.
2. Description of the Related Art
In a semiconductor wafer manufacturing process, a polishing apparatus is commonly used to provide a flat mirror polished surface on wafers. Such a polishing apparatus comprises a turntable and a top ring independently rotated relative to each other, and a wafer held on the underside of the top ring is polished by pressing the wafer against a polishing surface provided at the top surface of the turntable while supplying an abrasive liquid onto the surface. The polishing apparatus also includes a wafer storage unit for placing a cassette including wafers to be polished, a cleaning unit for cleaning and drying the polished wafers, and a transport apparatus for transporting the wafers between the processing units.
An example of such transport apparatus is shown in FIG. 11. The apparatus comprises a cylindrical robot body 10 and a set of arm devices 21 disposed on the top surface of the robot body 10. Each arm device 21 comprises two arms 25, 27 having articulating joint sections 35, 37, and the upper arm 27 is provided with a hand member (workpiece holding section) 41 disposed at the tip end of a connection member 33 through an articulating joint section 38.
An example of the configuration of the hand member is shown in FIG. 12. The hand member 41 is substantially plate-shape and has a recess in its central region serving as a receiving section 81 which is surrounded with protruding guides 83. The receiving section 81 comprises a wafer contact surface 85 for abutting the lower surface edges of a wafer W, and a bottom section surface 87 which is disposed inwardly of the wafer contact surface 85 at a lower level than the wafer contact surface 85. On the other hand, a top ring 90 is of a circular shape, and is provided with a bottom vacuum suction surface 91 and a guide ring 97 attached to its periphery.
To transfer the wafer W from the top ring 90 to the hand member 41 of such an arrangement, the hand member 41 is placed directly below the top ring 90 holding the wafer W by vacuum suction, and then the vacuum hold on the wafer is released by shutting off the vacuum suction so that the wafer W will drop into the receiving section 81 of the hand member 41. This operation is illustrated by designating the hand member 41 with single dot lines in the top portion of FIG. 12. After dropping the 25 wafer W, the hand member 41 is moved away downwardly.
This type of robotic transport apparatus is used to transport the wafers W to various processing apparatuses for various processing steps, such as polishing and cleaning steps, by means of the connection member 33. The wafers are often dripping with processing liquid, and in transporting wet wafers liquid droplets falling from the wafers of ten accumulate on the top surface of the robot body 10.
When the quantity of liquid droplets increases to fill the gap surrounding the articulating joint section 35, as illustrated by shaded areas 39 in FIG. 11, the liquid can penetrate into the arm 25 and robot body 10 through crevices in the joint section 35. Such seepage of liquid leads to corrosion of the mechanisms to generate malfunctioning of the working parts, leading to increased requirements for maintenance. Such operational problems lower the cost performance ratio of the apparatus and lead to loss of productivity. The same problems occur when the liquid seeps into joint sections 37, 38.
To prevent such seepage of liquid, a usual practice is to use mechanical seals, however, such contact seals have still some clearance and are not totally water tight, and it has been extremely difficult to prevent such liquid seepage into critical operating components of the apparatus. Furthermore, when O-rings, which are known to provide effective contact sealing, are used to seal joint section 35, 37 or 38, although the seepage clearance is reduced by the strong elastic sealing force of the O-rings, the local frictional forces are increased owing to the large frictional forces exerted by the compressed O-rings. The result is a drop in the operational speed of the arms 25, 27. On the other hand, if the speed of the arms 25, 27 is to be maintained, it is necessary to provide a larger torque for arm rotation, thus generating a problem of need for a driving motor with a larger driving capacity.
Also, the conventional design of the guide member 83 is such that the upper edge thereof is formed at right angles to the vertical, and if there is a misalignment between the top ring 90 and the hand member 41, the outer periphery of the wafer W can easily become lodged in the angular section of the guide member 83, thus preventing the wafer W from being safely deposited within the receiving section 81.
Another problem with the existing design of the robotic transport apparatus for handling the wafers is that the bottom section surface 87 of the hand member 41 often becomes contaminated with droplets 99 of liquid from sources such as abrasive liquid. Droplets 99 form spheres due to the surface tension on the bottom section surface 87 as illustrated in FIG. 12, and the diameter of such a sphere may exceed the separation distance between the wafer contact surface 85 and the bottom section surface 87 which commonly is only about 1.5 mm. Therefore, the droplet 99 could easily grow to contact the surface of the wafer W. It can be seen that if a hand member 41, having such large droplets 99 of abrasive liquid, is used to pickup a wafer W from a cleaning device, it can lead to a problem that the cleaned wafer has now become contaminated with the substances in the abrasive liquid.